/**
*      author: Y_Yao
*      created: 2025-03-01 12:05:34
**/

#include<bits/stdc++.h>

#define int LL
using namespace std;
using LL = long long;
const LL LLINF = 1e18;
const int INF = 0x3f3f3f3f;
int Q,H,S,D,N;

void solve()
{
    cin >> Q >> H >> S >> D >> N;
    H = min(2 * Q,H);
    S = min(2 * H,S);
    //cout << Q << " " << H << " " << S << " " << D << endl;
    if(2 * S <= D)
    {
        int ans = N * S;
        cout << ans << endl;
        return;
    }
    else
    {
        int cnt = N / 2;
        int r = N % 2;
        int ans = cnt * D + r * S;
        cout << ans << endl;
    }

}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}